This invention relates to an electrically insulated propane fuel tank such as is used with hot air balloons to provide fuel to a burner which burns the fuel and projects heat into the balloon envelope. The fuel tank according to the invention described in this application is adapted to be used in connection with hot air balloons but can also be used for other applications, such as with propane powered forklift trucks, gas grills and recreational vehicles. In aviation use, the tanks are manufactured in compliance with 49 C.F.R. .sctn.178.
The particular utility and need of this invention in connection with hot air balloons arises out of the often disastrous consequences of inadvertent contact between a hot air balloon and electric power lines, particularly upon descent of the balloon. The balloon carriage is an open structure, and even though the fuel tanks are generally recessed somewhat under a control panel or overhang, contact between electric power lines and fuel tanks is a possibility. Direct contact between power lines and fuel tanks can provide a fatal electric shock to one touching the fuel tank, or some other structure or object which itself is in contact with the fuel tank. In addition and more importantly, very close proximity without contact between high voltage power lines and the fuel tanks can cause an arc between the lines and the tank. The line and the tank become electrodes, and when the arc is struck between the two, the atmospheric gases between them ar ionized. Ionized gas has a very low resistance to current flow. High current flow generates such high heat that very quickly the metal of the fuel tank "puddles", causing penetration of the fuel tank and detonation of the pressurized gas in the tank, with disastrous consequences.
Due to the dangers of inadvertent contact between hot air balloons and power lines, research and development is taking place to determine ways to eliminate as much metal as is possible from the balloon. In other instances, as here, where the use of metal is necessary, efforts are being made to protect the metal against contact with sources of electric current.